The present invention is directed to a method for making a stopper. In particular, the present invention is directed to a method for making a stopper by providing a first stopper member having an upper surface including a concave portion. The first stopper member is positioned in a tool and a second tool is disposed over the first tool, whereupon a polymeric material is transferred through the second tool such that the polymeric material flows into the concave portion of the upper surface of the first tool.
Stoppers are typically used in the pharmaceutical industry for the purpose of providing a fluid-tight closure for a container such as a vial. Stoppers ordinarily are constructed from polymeric materials having moduli of elasticity selected such that a hypodermic syringe needle can be used to pierce the stopper for the purpose of injecting and/or withdrawing fluid from the container and such that the stopper fluidly seals the insertion channel formed by the hypodermic syringe needle when the needle is withdrawn therefrom. In this way, such stoppers maintain a fluid-tight sterility barrier between the contents of the container and the surrounding environment.
Some pharmaceutical products have characteristics that present an increased likelihood of interaction between the pharmaceutical product and the polymeric stopper. Such interaction can result in a release by the polymeric stopper of chemicals and/or particulate, thereby potentially compromising the safety and/or efficacy of the pharmaceutical product. In some cases, the resulting degradation of the stopper may be so significant as to compromise the sterile seal created by the polymeric stopper. For example, pharmaceutical products having a high pH may interact with certain rubber stoppers, thereby causing the release of chemicals and/or particulate from the stopper into the high pH pharmaceutical product. It has been found that this problem can be overcome by providing a layer of inert material, e.g., polytetrafluoroethylene, between the pharmaceutical product and the rubber material used to manufacture the stopper. The layer of inert material protects the rubber stopper from the pharmaceutical product, thereby preventing degradation of the stopper.
Processes for manufacturing laminated stoppers have been disclosed. For example, U.S. Pat. No. 4,389,271 to Shandy, et al. and U.S. Pat. No. 4,398,989 to Allen, et al. disclose methods for making polytetrafluoroethylene-laminated stoppers of the type above-discussed. The '989 patent discloses a system for making a molded article having a body portion constructed of an elastomeric material and a liner portion constructed of an inert material, the liner portion covering a portion of the peripheral surface of the body portion. The molded article is produced by bonding a layer of elastomeric material to a layer of inert material and forming a disc from the resulting laminated sheet. The disc is then placed into a molding cavity such that the layer of inert material faces the lower surface of the molding cavity. Uncured elastomeric material is then charged into the molding cavity over the top of the disc. The resulting stopper is then cured and removed from the molding cavity.
The '271 patent discloses a method in which a sheet of laminated material including an elastomeric layer and an inert layer is partially cut to form a disc. The sheet containing the partially cut discs is then positioned over a transfer plate such that the partially cut discs are in registry with openings in the transfer plate. The transfer plate then is positioned over a plurality of molding cavities such that the openings in the transfer plate are in registry with the molding cavities. The discs are then completely severed from the sheet and transferred through the openings in the transfer plate and into the molding cavities. Uncured elastomeric material is then charged into the molding cavities over the top of the discs. The resulting stoppers are then cured and removed from the molding cavities.
One drawback in producing laminated stoppers in accordance with the methods disclosed in the '989 and '271 patents is that uncured elastomeric material charged into the molding cavity containing the disc tends to flow between the molding cavity and the inert surface of the disc. As a result, a portion of the inert material may be coated with a layer of the elastomeric material after the resulting stopper is cured. When the stopper is used to seal a pharmaceutical container, the elastomeric material will be exposed to the pharmaceutical product, thereby creating a possibility for interaction between the elastomeric material of the stopper and the pharmaceutical product.